No abstract

Pressure swing adsorption (PSA) experiments are carried out in a 2-column laboratory setup using activated carbon. As feed an equimolar CO2/H2 mixture is used. Adsorption pressures of 10, 20, and 30 bar are applied, whereas the desorption pressure and the feed temperature are fixed at 1 bar and 25 °C, respectively. During the experiments the temperatures at five different locations inside the columns are measured and the composition of the product streams is analyzed by a mass spectrometer. A one-dimensional, nonisothermal, nonequilibrium model is used to reproduce the experiments. The model was validated previously using breakthrough experiments, and the modifications required to describe full PSA cycles are highlighted. It is shown that the temperatures measured inside the columns provide an excellent possibility for comparison of experiments and simulations, whereas the measured concentration profiles are affected by the piping between column outlet and MS, which has to be considered carefully.

In this work, the adsorption of water vapor on a commercial activated carbon is studied by means of static and dynamic measurements. To this end, two customized setups are used, which are able to deal with the challenges associated with adsorption measurements under humid conditions. In the first part, the equilibrium of water vapor on activated carbon during adsorption and desorption at 45 °C is characterized. The equilibrium adsorbed amount of water vapor exhibits a pronounced hysteresis loop, requiring the use of an isotherm model with hysteresis to describe the data. In the second part, fixed-bed experiments for both adsorption and desorption conditions at three feed velocities are presented. These dynamic experiments are described by a nonisothermal detailed column model, which considers the linear driving force model for mass transfer and axial dispersion. Heat and mass transfer coefficients are estimated so as to describe the fixed-bed experiments. The results from the static and dynamic measurements are shown to be consistent with each other for both adsorption and desorption conditions, provided the hysteretic behavior of the adsorption equilibrium is considered. Finally, it is shown that the use of an average value for the mass transfer coefficient results in good agreement between experiment and simulation, and the improvement due to a more complex model is minimal.

Temperature swing adsorption (TSA) processes are considered as an interesting option for the capture of CO2 from flue gases. In this work, a shortcut model is developed for a four step cycle aimed at recovering the more retained component at high purity from a binary mixture, e.g. CO2 from CO2/N2. The model equations, which assume local adsorption equilibrium but take into account heat transfer kinetics, enable a direct semianalytical solution of the cyclic steady state. For fixed temperatures of the indirect heating and cooling fluid, interstitial velocity, and feed composition, the remaining operating conditions can be reduced to the high and low temperature levels achieved during the cycle, which control the thermodynamic states defining the effective cyclic capacity. This model is used to investigate the CO2/N2 separation by TSA on a commercial zeolitic adsorbent. Important trends are revealed by performing a parametric analysis of the operating conditions on the relevant quantities, that is, purity, recovery, specific thermal energy consumption, and productivity. Optimal operating conditions are localized within the region of feasible operating conditions and a trade-off between productivity and specific energy consumption is presented and discussed. Besides providing insight into TSA processes for the recovery of the heavy component, this tool could be used for rapid yet robust sorbent screening.

A mathematical model used to describe cyclic adsorption processes is calibrated and validated for the simulation of temperature swing adsorption (TSA) processes applied to the capture of CO 2 from a model flue gas (CO 2 /N 2 ) using zeolite 13X as sorbent material. Three types of experiments are reported in this work, all of them performed in jacketed columns packed with 13X. During these experiments, the temperature was measured at five positions along the central axis of the column, and the exit composition was measured on line by mass spectrometry. The first series of experiments were breakthrough experiments, used to characterize transport phenomena within the packed bed. The second series were heating and cooling experiments, which were used to study the heat transfer from the heating fluid in the column jacket to the bed. Lastly, cyclic TSA experiments were performed to test the model's ability to predict the cyclic steady state behavior of the column as well as the separation performance of the process.